They use both radiotherapy and also, what is known as systemic therapy. This includes chemotherapy, hormone therapy and biological agents, all of which are used to treat cancer. Technologies in the field of clinical oncology are developing rapidly. For example, some tumors can be treated with highly sophisticated precision external beam radiation therapy such as proton beam therapy. Clinical oncologists determine which treatment to use by considering a range of factors including tumor type, the site of the tumor, the stage of the disease and the patient’s general health. They then assess the relative merits of different treatments before presenting these to the patient so that an informed decision can be made. 
The actual cancer diagnosis is usually given by another specialist, but it is with the clinical oncologist that the patient can ask important questions about their condition and treatment. Helping patients to come to terms with their condition and treatment is a vital part of the work. You’ll also spend time in the radiotherapy department, working alongside colleagues and planning individual radiotherapy treatments. These individual patient plans are also a very important part of your work.